Hand sanding tool

ABSTRACT

A hand grinder ( 10 ), having a grinding sheet ( 20 ) that fits over the grinding disk underside ( 18 ) and having clamping means ( 22, 24, 30 ) for fixing the grinding sheet ( 20 ) to the grinding disk ( 14 ), the clamping means ( 22, 24, 30 ) having clamping bodies ( 24 ) that can be pressed against the ends ( 21 ) of the grinding sheet; the clamping body is supported freely rotatably about an eccentric shaft ( 28 ), and the pivot shaft ( 28 ) is located substantially vertically above a concavely curved mounting face ( 22 ).

PRIOR ART

The present invention is based on a hand grinder as generically definedby the preamble to claim 1.

From British Patent Application GB 2 322 582, a motor-driven handgrinder is known which is provided with a system for clamping andtightening, i.e. making taut, a grinding sheet that can be mounted onthe underside of its grinding disk. This system functions reliably andis easy to manipulate, but the effect of making the grinding sheet tautis relatively limited, and hence a perceptible relative motion betweenthe grinding sheet and the grinding disk cannot be precluded.

ADVANTAGES OF THE INVENTION

The invention having the characteristics of claim 1 has the advantagethat an inexpensive hand grinder is created that by simple means enableshighly effective clamping and at the same time effectively making thegrinding sheet taut on the grinding disk, in which a relative motionbetween the grinding sheet and the grinding disk is as good asprecluded, and because the pivot shaft of the clamping body is locatedsubstantially vertically above the clamping point, on top of thegrinding disk above the mounting face, and because the mounting facespaced apart from pivot shaft in a defined way is curved, an especiallylong slaving path is provided for making the grinding paper taut.

Because the clamping body is equipped as a cylindrical roller, and theassociated region of the top of the grinding disk is equipped as aconcave hollow-cylindrical groove, upon pivoting of the clamping bodywhat occurs first is a thrusting slaving of the grinding sheet on thetop of the grinding disk, until it is made as taut as is maximallypossible. Upon displacement of the grinding sheet, the contact pressurebetween the clamping body and the mounting face of the grinding disksimultaneously increases considerably, so that when the highest clampingand locking force is reached, while the end of the grinding sheet isfirmly held, a maximum tightening effect prevails at the same time.

Because the clamping body is provided with a plastic hose as itsfriction lining, and in particular one carried by a metal core, aclamping body of simple construction with a good grip is created.

Because the metal core of the clamping body firmly holds one clampinglever each, particularly on both of its axial ends, in a way securedagainst relative rotation and in captive fashion, particularly by meansof radial and axial bores into which the clamping lever can be insertedor placed, the clamping body is especially sturdy and is capable oftransmitting strong tightening and clamping forces uniformly and gentlyand in a positionally secured way to the grinding sheet.

Because the clamping lever can be locked in a spring-prestressed fashionin its clamping position, particularly by an end remote from the edge,the clamping force on the grinding sheet does not lessen.

Because the metal core has axial grooves on its circumference, and towhich the bent-over regions of the slaving levers can be placed andextend with flush contours with the core, the slaving levers are mountedespecially securely by the plastic hose slipped over the core.

Because the mounting face extends at an angle to the pivoting path ofthe clamping body that is close to self-locking, especially secureclamping of the grinding sheet, yet with easy release, is possible.

Because in the release position of the clamping body, there is a slitbetween the clamping body and the mounting face, into which slit the endof the grinding sheet can be inserted beneath and/or onto the clampingbody, the grinding sheet can be clamped especially securely.

Because the mounting face is curved, in particular in concave fashion,and extends toward the outermost pivot circle, leading to the shaft, ofthe clamping body in the region near the edge of the grinding disk witha spacing amounting to several millimeters and intersects the pivotcircle in the region remote from the edge, a stop for the clamping bodyis created with which secure clamping of the grinding sheet is possible.

Because the clamping body has at least two eccentric cams, which inparticular are on the order of round teeth and which extend parallel toits shaft and/or to the top of the grinding disk over the width of theclamping body, the radius of which eccentric cams relative to the pivotshaft is greater than the spacing between the pivot shaft and themounting face, the latter in particular extending rectilinearly andsmoothly, the grinding sheet can be tightened especially securelydirectly after being clamped.

Because the clamping body, and in particular its eccentric cams and/orthe mounting face—at least in part—comprise elastically deformablematerial—the clamping device is automatically adaptable to grindingsheets of different thickness that are to be clamped.

Because a threshold, which in particular is rounded, is located on thefront and rear edge of the grinding disk and by way of it the end of thegrinding sheet can be guided such that this end is located in floatingfashion between the threshold and the mounting face, and after beingclamped it can be made taut by simply pressing down on the floatingregion.

Because between the front and rear edges on the top of the grinding diskthere is an indentation in the grinding disk, into which the grindingsheet guided over it can be pressed, and the indentation is elasticallyspanned, in particular by a leaf spring, the grinding sheet after beingclamped can be made taut by pressing down on its region located infloating fashion.

Because the leaf spring can be pressed jointly with the grinding sheetinto the indentation by means of the second eccentric cam, it is notonly made taut but also reliably clamped at a further point.

Because the second eccentric cam has a greater diameter than the first,it forms a rotation stop, past which the clamping body cannot be rotatedfarther, and which defines the clamping position of the clamping body.

Because the first eccentric cam, in the clamping position, is located atleast 2 mm in front of and parallel to the vertical extending from thepivot shaft to the mounting face, and in the process the eccentric camsare braced, spreading away from one another, on the mounting face, theclamping position is adjustable in overlocking fashion in a markedlyperceptible way and can be released in overlooking fashion only counterto a resistance, precluding an unintentional release.

DRAWING

The invention is described in further detail below in terms of anexemplary embodiment and in conjunction with the drawing.

Shown are

FIG. 1, a three-dimensional view of the hand grinder of the invention;

FIG. 2, a detail of the hand grinder showing the clamping means forclamping the grinding sheet;

FIG. 3, a three-dimensional of the detail of FIG. 2 in the clampingposition;

FIG. 4, the view of FIG. 3 in the open position;

FIG. 5, a further variant of the grinding sheet clamping device in therelease position;

FIG. 6, the grinding sheet clamping device of FIG. 5 in the clampingposition;

FIG. 7, a grinding disk with grinding sheet clamping devices as in FIG.5; and

FIG. 8, the geometric detail of a clamping roller of FIGS. 5 and 6.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

A hand grinder 10—a hand-held vibrating grinder—shown laterally from thefront in FIG. 1 has a housing 12, whose upper region serves as a handle13 and whose lower region has a grinding disk 14, which can be driven bya motor to vibrate and to whose underside 18 a grinding sheet 20 can besecured. The grinding sheet 20, with two diametrically opposite ends 21,wraps around the front and rear edges 15, 17 of the grinding disk 14.The ends 21 of the grinding sheet each protrude for some distanceparallel to the top 16 of the grinding disk 14 toward its center. Theends 21 of the grinding sheet can be clamped in such a way as to makethem taut between a mounting face 22 on the top 16 and clamping roller24. The clamping roller 24 is pivotable by means of a clamping lever 30.The clamping lever 30 extends, bent 90°, from the clamping roller 24parallel to the length of the grinding disk 14. The end of the clampinglever 30 is pivotable upward, in the viewing direction, into theclamping position of the clamping roller 24, or in other wordscounterclockwise, and can be locked in elastically prestressed andoverlooking fashion to the top 16 in an abutment 31 in the clampingposition.

The grinding sheet 20, on its underside, has a layer 44 of abrasive,which when the grinding sheet 20 is placed between the clamping roller24 and the mounting face 22, in the placement direction indicated by thearrow 42, faces toward the clamping roller 24. From the roughness of theabrasive layer 44, especially good adhesion exists upon contact with theclamping roller 24, so that upon pivoting of the clamping roller 24 intothe clamping position, the end 21 of the grinding sheet is carriedalong, adhering to the clamping roller, and is then securely clampedagainst being lost. The grinding sheet 20 is fixed to the underside 18of the grinding disk 14 in such a way that it is made taut and issecured against relative motion. As a result, the grinding stroke of thegrinding disk 14 is transmitted to the grinding sheet 20 without slipand with high efficiency. The removal power in grinding iscorrespondingly high, creating a constantly homogeneous grinding patternthat is virtually independent of the contact pressure with which thehand grinder is pressed against a workpiece to be machined.

FIG. 2 shows an enlarged detail of the right-hand side of the frontregion of the grinding disk 14. A bearing block 32 protrudes past itstop 16 on each side and, with a central bore not identified by referencenumeral, receives a pivot shaft 28 of the clamping roller 24, aboutwhich shaft this clamping roller is pivotably supported. A rigidlysecured clamping lever 30 protrudes from the clamping roller 24 and isbent at a right angle to the pivot shaft 28. In the clamping position ofthe clamping roller 24, it extends parallel to the length of thegrinding disk and is lockable in overlooking or spring-prestressedfashion to a bearing-blocklike abutment 31 on the top 16 of the grindingdisk. In this final position of the clamping lever 30, the clampingroller 24 is in its outermost left-hand pivoted position, in which itrests on the stoplike pressure region 26 that rises in concave fashionon the mounting face 22, and firmly holds a grinding sheet that isclamped between the clamping roller 24 and the mounting face 22.

In this clamping position, the center 36 of curvature of the clampingroller 24 has a position located near the center of curvature of themounting face 22. The curvature profile 38 of the mounting face 22 issubstantially equivalent to the radius 37 of curvature of the clampingroller 24. The mounting face 22 is located in the pivot circle of theclamping roller 24 such that it forms a stop with the negative contourof the clamping roller 24. As a result, a large surface area of theclamping roller 24 rests on the mounting face 22, or the pressure region26.

The front edge 15, located on the right in the viewing direction, of thegrinding disk 14 is curved in convex form in longitudinal section, sothat a grinding sheet 20 wrapped around it can slide away past itrelatively easily, without the threat of tearing.

The mounting face 22 extends from the front edge 15 to the pressureregion 26 in such a way that opposite the pivot circle of the clampingroller 24, it forms an acute-angled slit 46. The grinding sheet 20 canenter this slit 46 between the clamping roller 24 and the mounting face22, if the clamping roller 24 is pivoted far enough counterclockwise andupward about the shaft 28—that is, in the release direction. If then,after the grinding sheet 20 is put in place, the clamping roller 24 isrotated clockwise about the shaft 28 back into its clamping position,then initially it pulls the grinding sheet 20 in slaved fashion alongwith it via the mounting face 22, until together with the end 21 of thegrinding sheet it comes to rest on the pressure region 26 of themounting face 22 and firmly holds the grinding sheet 20 securely taut,in captive fashion. By clamping and the end 21 of the grinding-sheet onboth the front and the rear edges 15, 17 of the grinding disk 14 andmaking it taut, the grinding sheet 20 is made taut twice and is fixed ina way secure against shifting relative to the underside 18 of thegrinding disk. Slip-free grinding with high efficiency is thus possible,because a relative motion of the grinding sheet 20 with respect to thegrinding disk 14 is precluded.

For removal of the grinding sheet 20 from the grinding disk 14, theclamping lever 30 is pivoted laterally outward and farther downward outof its locked position in the abutment 31. In the process, the clampingroller 24 moves with it counterclockwise, whereupon the slit 46increases in size, and finally the end 21 of the grinding sheet isreleased, so that the grinding sheet 20 is easily removable.

FIG. 3 shows a three-dimensional view of the details, substantiallyexplained in conjunction with FIG. 2, of the front edge 15—seen from theleft-hand side; this need not be explained in every detail again here.The clamping roller 24 has been pivoted into its clamping position, inwhich it firmly clamps the end 21 of the grinding sheet 20 at theconcave mounting face 22 and secures it against being lost.

The clamping roller 24 is joined in a manner fixed against relativerotation to an eccentric pivot shaft 28 above the pressure region 26,and the pivot shaft 28 changes over, on both sides of the clampingroller 24, in each case after a bend into a respective clamping lever30. Each clamping lever 30 may comprise spring wire, so that theclamping roller 24, in its clamping position, presses the end 21 of thegrinding sheet against the pressure region 26 in spring-prestressedfashion.

FIG. 4 shows the same region of the grinding disk 14 and the clampingroller 24 as in FIG. 3, but in the “open” position, in which the slit 46between the mounting face 22 and the clamping roller 24 is so large thatthe end 21 of the grinding sheet can conveniently be inserted far enoughthat when the clamping roller 24 is pivoted downward this end is carriedalong by the clamping roller 24 and thrust along the mounting face 22—tothe right in the viewing direction—and finally becomes clamped in itsfinal position in the pressure region 26 of the mounting face 22. Theclamping levers 30 are oriented perpendicularly downward in this state,and in this position they keep the clamping roller 24 in its “open”position.

FIG. 5 is a side view of a further exemplary embodiment of a grindingdisk 140, which on its underside 180 has a grinding sheet 200 extendingparallel to the underside; with its end 210, this grinding sheet iswrapped around the front edge 150 of the grinding disk 140 and guidedover its top 160 in such a way that it is positioned between the top 160and the circumference of a partly cylindrical clamping roller 54. Theclamping roller 54 is supported rotatably about a pivot shaft 280 in abearing block 320, and with an axial annular collar 55 it reachesthrough a fittingly circular recess, acting as an abutment 310, in thebearing block 320. Two eccentric cams 56, 57 are located on thecircumference of the clamping roller 54, parallel to the shaft 280 ofthe clamping roller 54; the first eccentric cam 56 extends remote fromthe edge toward the front edge 150 and has a markedly lessereccentricity—measured relative to the pivot shaft 280—than the secondeccentric cam 57, which is seated in the region near the edge of theclamping roller 54. The two eccentric cams 56, 57 are spaced apart fromone another by one tooth gap 59.

The clamping roller 54 can be pivoted by hand toward the grinding disk140 into its clamping position by means of a clamping lever 60 thatpoints radially outward, toward the front edge 150. In this pivotingprocess, the eccentric cam 56 remote from the edge is first thrust overthe end 210 of the grinding sheet and pulls it, making it taut, to theright across the top 160 of the grinding disk 140, until the secondeccentric cam 57 is pivoted downward and is braced on the end 210 of thegrinding sheet, or on the top 160 of the grinding disk 140. Since theend 210 of the grinding sheet spans a threshold 64 of partly cylindricalor rounded cross section, this end is located in floating fashionbetween the threshold 64 and the first eccentric cam 56, until itpresses the second eccentric cam 57 down onto the top 160. Pressing thefloating grinding sheet region downward onto the top 160 of the grindingdisk 140 by means of the second eccentric cam 57 draws the grindingsheet 200 farther to the right in the longitudinal direction and thusmakes it still more taut. It is assumed here that the end 210 of thegrinding sheet, positioned on the rear edge 170, not also shown here,diametrically opposite the front edge 150 was fixed beforehand, becauseotherwise, or in other words upon yielding of the diametrically oppositeend of the grinding sheet, the tightening is undone.

FIG. 6 shows the clamping roller 54 of FIG. 5 in the “closed”position—unlike FIG. 5, which shows it in the “open” position. The firsteccentric cam 56, remote from the edge, is positioned approximately 2 mmto the right of the pivot shaft 280, in the viewing direction, and thesecond eccentric cam 57, near the edge, is braced via the grinding sheet200, or its end 210, on the top 160 of the grinding disk 140. The secondtightening step is thus completed, in which the end 210 of the grindingsheet is pulled to the right in the viewing direction across thethreshold 64 and kept taut.

By making the grinding sheet taut twice on both ends 150, 170 of thegrinding disk 140, a relative motion between the grinding sheet 200 andthe underside 180 of the grinding disk 140 is especially reliablyprevented, so that as the grinding disk 140 moves back and forth over aworkpiece, especially effective grinding is possible.

The grinding disk 140 of FIGS. 5 and 6, shown in FIG. 7 as athree-dimensional top view, has on each of its two ends an identical,partly cylindrical clamping roller 54, whose clamping levers 60 areoriented toward the front edge 150 and rear edge 170, respectively, andcan easily be pivoted slightly downward into the clamping position byhand, in particular using the thumb.

For releasing the grinding sheet 200, the clamping levers 60 should bepivoted upward in the viewing direction, so that the eccentric cams 56,57 open up a gap between the top 160 of the grinding disk 140 and theclamping roller 54, out of which gap the end 210 of the grinding sheetcan easily be removed.

FIG. 8 shows a schematic cross section of a clamping roller 54, pivotedinto the clamping position, in which the first eccentric cam 56, remotefrom the edge, braces the end 210 of the grinding sheet on the mountingface 62 of the top 160 of the grinding disk 140. The eccentric cam 56has a parallel spacing 63 of a few millimeters from the plumb linedropped from the pivot shaft 280 to the mounting face 260 so that aprestressed position of the clamping roller 54 is thus accomplished. Theclamping roller 54 comprises elastic material. Its overlooking istherefore possible by elastic deformation of the first eccentric cam. Itmay furthermore be advantageous if the mounting face 62 likewisecomprises elastically deformable material, on which the end 210 of thegrinding sheet and the two eccentric cams 56, 57 are braced. As aresult, different thicknesses of grinding sheet can be clamped in a waythat makes them taut, with the same secure hold, regardless of theirmasses.

The first eccentric cam 56, in its clamping position after itsoverlooking, builds up an elastic prestressing force relative to themounting face 62 with which it presses the second eccentric cam 57against the top 160 of the grinding disk 140, and the latter presses theend 210 of the grinding sheet downward with precisely this prestressingforce into an indentation 66 and thus additionally afterward. Theindentation 66 may be spanned by elastic means, such as plastic or aleaf spring.

Instead of a clamping lever 60 integrated with the clamping roller 54and pointing outward toward the grinding disk edge 150, 170, a clampinglever may be located as shown in FIGS. 1 through 4, which in theclamping position points in each case toward the center of the grindingdisk 140, where it is lockable in overlooking fashion.

1. A hand grinder (10), having a grinding sheet (20) that fits over thegrinding disk underside (18) and having clamping means (22, 24, 30) forfixing the grinding sheet (20) to the grinding disk (14), the clampingmeans (22, 24, 30) having clamping bodies (24) that is pressable againstthe ends (21) of the grinding sheet, wherein the clamping body (24) isrotatably supported about a shaft (28) located substantially verticallyabove a mounting face (22).
 2. The hand grinder according to claim 1,wherein the clamping body (24) is designed as an in particularcylindrical roller, and the mounting face (22) is designed as a groovethat is cylindrical at least in one portion.
 3. The hand grinderaccording to claim 1, wherein the clamping body (24) has a frictionlining, in particular a plastic hose, on its circumference.
 4. The handgrinder according to claim 1, wherein the clamping body (24), on thecylindrical core (25) which in particular is of metal, supports a bentclamping lever (30, 60), in particular such that the contours are flush,in a manner fixed against relative rotation and in captive fashion. 5.The hand grinder according to claim 1, wherein an end, remote from theedge, of the clamping lever (30) is lockable in its clamping position inan elastically prestressed, in particular overlooking way.
 6. The handgrinder according to claim 1, wherein the clamping lever (30) is coupledto the core (30) of the clamping body (24), placed in radial and axialbores.
 7. The hand grinder according to claim 6, wherein the clampingbody (24) has one clamping lever (30) on each of its axial ends.
 8. Thehand grinder according to claim 6, wherein the clamping body (24),particularly on its metal core (25), has radial and axial grooves, intowhich the clamping lever (30), made particularly of spring wire, isplaceable flush with the contour of the metal core (25) and is coupledto the clamping body (24) in a manner fixed against relative rotation bymeans of the plastic hose (23).
 9. The hand grinder according to claim8, wherein in the release position of the clamping body (24), there is aslit (46) between the clamping body and the mounting face (22), intowhich slit the end (21) of the grinding sheet is insertable beneathand/or onto the clamping body (24).
 10. The hand grinder according toclaim 1, wherein the mounting face (22) is curved, in particular inconcave fashion, and extends toward the outermost pivot circle, leadingto the shaft (28), of the clamping body (24) in the region near the edgeof the grinding disk (14) with a spacing amounting to severalmillimeters and intersects the pivot circle in the region remote fromthe edge.
 11. A hand grinder (10), having a grinding sheet (20, 200)fitting over the underside (18, 180) of its grinding disk (14, 140), andhaving clamping means (24, 22, 54, 62) for firmly clamping the grindingsheet (20, 200) to the grinding disk (14, 14), the clamping means (24,22, 54, 62) having clamping bodies (24, 54, 56, 57) that are pressableagainst the ends (21, 210) of the grinding sheet, wherein the clampingbody (54, 56, 57) has at least two eccentric cams (56, 57), which inparticular are on the order of round teeth and which extend parallel toits shaft (28, 280) and/or to the top (160) of the grinding disk (140)over the width of the clamping body (24, 54), the radius of whicheccentric cams relative to the pivot shaft (28) is greater than thespacing between the pivot shaft (28) and the mounting face (22, 62), thelatter in particular extending rectilinearly and smoothly.
 12. The handgrinder (10) according to claim 1, wherein the clamping body (24, 54),and in particular its eccentric cams (56, 57) and/or the mounting face(22, 62)—at least in part—comprise elastically deformablematerial—adaptable to grinding sheets of various thickness that are tobe clamped.
 13. The hand grinder (10) as generically defined by thepreamble to claim 11, wherein a threshold (64), which in particular isrounded, is located on the front and rear edge (150, 170) of thegrinding disk (140) and positions the end (21) of the grinding sheet infloating fashion between the threshold (64) and the mounting face (62).14. The hand grinder (10) as generically defined by the preamble toclaim 11, wherein the grinding disk (14, 140), between its front andrear edge (15, 17, 150, 170) has an indentation (66) on the top (16,160), into which indentation the grinding sheet (200) guided above it ispressable, in particular with the end (21) of the grinding sheet fixed,and the indentation is spanned, in particular by elastic means,preferably a leaf spring.
 15. The hand grinder (10) according to claim1, wherein the elastic means are pressable jointly with the grindingsheet (200) into the indentation by means of the second eccentric cam(57).
 16. The hand grinder (10) according to claim 1, wherein the secondeccentric cam (57) forms a rotation stop, past which the clamping body(54) is not rotatable further, and which has a greater radius—measuredbetween the pivot shaft (280) and the end of the eccentric cam (57)—thanthe first eccentric cam (56).
 17. The hand grinder (10) according toclaim 1, wherein the first eccentric cam (56), in the clamping positionof the clamping body (54), is located at least 2 mm in front of andparallel to the vertical extending from the pivot shaft (280) to themounting face (62), and in the process the eccentric cams (56, 57) arebraced, spreading away from one another, on the mounting face (62).